Many applications requiring regulated fluid flow utilize valves that open different amounts in response to one or multiple factors. Such a valve may be actively controlled via an electronic controller. Alternatively, passive control is sometimes possible, such as with a valve having a thermostatic element that varies its opening with changes in fluid temperature.
One application that has utilized flow control valves is a vehicle transmission. Vehicle transmissions typically have rotating parts that require constant lubrication. A certain level of fluid is required to be maintained in the transaxle in order to ensure a proper operation of its hydraulic system. The fluid circuit often includes one or more pumps located within the side cover attached to a main housing with a suction inlet coming from the sump formed by a bottom pan. The oil level in the sump must be high enough to ensure that the pump has adequate suction, especially during extreme cold temperatures or certain maneuvers such as high acceleration turns that could cause the fluid to move away from the pump suction during the condition or turn. At the same time, it is desirable to keep the oil level as low as possible to reduce spin and windage losses associated with excess fluid in the rotating parts of the transmission. Generally, fluid flow increases with increasing temperature, so valves that gradually close with increasing temperature have been used to control the oil level in the bottom pan. However, with these valves, some minimum oil level, which is not optimal for reducing spin and windage losses, must always be present so that adequate oil is present at the pump even in the event that outside forces or conditions, such as a high g-force turn, shifts the bulk of the oil in the bottom pan away from the pump suction.